The present invention relates to a process for preparing a magnetic layer, particularly a process for preparing a magnetic layer suitable for magnetic recording and useful for an improvement of storage characteristics.
Further, the present invention relates to a magnetic head, particularly a magnetic head using as part of a magnetic pole a magnetic material having an extremely high saturation induction Bs (Bs=4.pi.Ms, wherein Ms is saturation magnetization) which is prepared according to the above-mentioned process.
A magnetic layer having a high saturation induction and a high permeability is suitable for improving recording characteristics in a magnetic recording device. For the purpose of obtaining this kind of magnetic layer, a layer (film) of a magnetic compound has heretofore been formed by a low vacuum deposition method, a gas atmosphere deposition method, a sputtering method, or the like as described in "Appl. Physics Lett." (Vol. 20, No. 12, P. 15 (1972)) or "Solid State Physics" (Vol. 7, No. 9 (1972)). However, these known thin film deposition technologies have a defect that they are so poor in reproducibility that they provide large lot-to-lot variation of recording characteristics between magnetic layers formed because of not only large scattering or variation of magnetic characteristics thereof but also a difficulty encountered in controlling ambient conditions, etc. during magnetic layer formation. Furthermore, since a magnetic compound is formed on a substrate in vacuo or in a gas atmosphere at once, no consideration has been given at all to the control of the composition and magnetic characteristics of the magnetic layer surface only in the desired areas.
The magnetic head will now be discussed as an instance of magnetic recording devices. The magnetic recording technique has been making a remarkable progress these years by virtue of development of magnetic tapes with high coercive force and high performance head materials for the above-mentioned tapes. Especially when a metal tape having a high coercive force is used, a remarkable increase in output and an increase in O/N (output to noise) ratio are attained in a high recording density area ranging from several .mu.m to 1 .mu.m in recording wave length. Thus a marked improvement in recording density is being attained in the fields of VTR, etc. where a high recording density is required. However, a magnetic head using ferrite which has heretofore been used in VTR, etc. does not have a sufficient recording magnetic field because the saturation induction of ferrite is about 5000 G or lower. Thus a magnetic head using a metal magnetic material having a high saturation induction has been demanded in using a metal tape with a high coercive force. Examples of such a metal magnetic material include an Fe-Al-Si alloy (saturation induction: about 10 kG), an Fe-Ni alloy (saturation induction: about 8 kG), an Fe-Si alloy (saturation induction: about 18 kG), systems of at least one of Fe, Co, and Ni containing B, C, N, Al, Si, P, etc. incorporated thereinto, and metal-metal amorphous alloy systems of at least one of Fe, Co, and Ni containing Y, Ti, Zr, Hf, Nb, Ta, etc. incorporated thereinto, of which an Fe-Si alloy having a Si content of about 6 wt. % is a material having the highest saturation induction of about 18 kG.
On the other hand, the gap length of the VTR magnetic head has become smaller and smaller these years for realizing high density magnetic recording. The conventional gap length of 0.5 .mu.m has recently been reduced to 0.3 .mu.m, which must be further reduced to 0.1 to 0.2 .mu.m in the future. When the gap length is reduced as described above, the strength of a stray field from the head is markedly decreased. Further, the coercive force of the magnetic recording medium is being increased steadily these years for realizing high density magnetic recording. The coercive force, about 300 Oe, of the conventional oxide type magnetic tape has been increased to about 700 Oe. Even a tape having a coercive force of about 1,500 Oe is now produced as a result of recent development of a magnetic tape using a metal magnetic powder. When a magnetic head having a small gap length as mentioned above is used with a magnetic tape having such a very high coercive force, there arises a problem of insufficiency of the recording capacity in a long wavelength area. Thus a magnetic head material having as high a saturation induction as possible is needed. In the future, the coercive force of the magnetic recording medium will be further increased while the gap length of the magnetic head will be further reduced. In view of such a trend, a high saturation induction will be more and more required of the magnetic head material.
As regards the magnetic head for perpendicular magnetic recording which has recently been increasingly studied, the thickness of the main pole with which recording and playback are made on the perpendicular magnetic recording material must be extremely reduced for improving the recording density. Where the main pole is extremely thin, magnetic saturation is liable to occur at the tip of the magnetic pole in recording. When magnetic saturation occurs, there arises a problem of a difficulty in recording on the perpendicular magnetic recording medium. To solve such a problem, the saturation induction of the magnetic material used in the main pole must be increased as much as possible.
The same problem is involved in the conventional thin film head for longitudinal magnetic recording which is employed in computer memories and the like. More specifically, since the thin film head has a small cross-sectional area of the magnetic pole in close proximity to the functional gap, magnetic saturation is apt to occur. Accordingly, also in the thin film head, a magnetic head material having a high saturation induction is eagerly demanded.